1. Field of the Invention
The present invention relates to a device that analyzes diffraction patterns resulting from reflection high-energy electron diffraction and an intensity analysis method, and it particularly relates to a halation-prevention filter that prevents diffraction pattern halation, an image analysis device equipped with the halation-prevention filter, and a diffraction pattern intensity analysis method and a diffraction pattern intensity correction program that use the halation-prevention filter.
2. Description of Related Art
Reflection high-energy electron diffraction is an analytical technique widely used in the molecular beam epitaxy field, as a technique for monitoring in real time the growth state, when growing crystals (e.g., metals, semiconductors) in vacuo.
In particular, ever since it was discovered that the atomic-layer-by-atomic-layer growth of crystals was observable by measuring the intensity of specular reflection point(s) in reflection high-energy electron diffraction, reflection high-energy electron diffraction has been recognized as a useful method for controlling crystal growth at the atomic layer level, so it has been applied to various industries (e.g., semiconductor device fabrication).
However, in image analysis devices that use the diffraction patterns resulting from conventional reflection high-energy electron diffraction, when a diffraction pattern is photographed, the intensities of the specular reflection point(s) are much greater than the intensities of the surrounding diffraction points and Kikuchi pattern, so the vicinity of the specular reflection point(s) produces halation. This becomes particularly significant when the entire diffraction pattern is photographed, and if the light exposure is decreased during photography in order to avoid halation, the following drawback results: the surrounding diffraction points and the Kikuchi pattern become unobservable because of the insufficient intensity (light intensity).
This problem frequently restricts, to the region between the specular reflection point(s) and the zero-order Laue zone, the conventional CCD camera-based observation of the diffraction pattern resulting from reflection high-energy electron diffraction, as the only way to avoid halation without decreasing the light exposure. However, when such an observation technique is used, the diffraction pattern information from outside the zero-order Laue zone is undetected, so a problem different from the aforementioned drawback is confronted: it is impossible to accurately analyze the sample state.
In a technique sometimes adopted in order to prevent the halation that occurs in a diffraction pattern when using a camera to photograph the diffraction pattern resulting from reflection high-energy electron diffraction, masking is performed when printing the photographic printing paper instead of in the photography state, thereby yielding a diffraction pattern with good contrast. This technique has a problem, however, in that linear intensity analysis is impossible because an irreversible correction is applied to the light intensity, which is essential for intensity analysis.
As another device configuration measure that prevents halation, there is a technique that uses sectors with a masking part and a transmissive part, between the fluorescent screen and the measurement sample in the vacuum chamber. To be more specific, in a sector, the masking part is configured by using a blade or vane with a geometrically computed shape. Furthermore, by making the electron beam, which is diffracted in the vicinity of the surface of the measurement sample, pass through the sector in which this blade rotates, the sector functions to inhibit halation near the center by physically decreasing the amount of electron beam passing through.
Actually, however, the mere adherence of minute dust particles on the blade markedly attenuates the intensity in the rotating part corresponding to this dust's position. An a result, this intensity attenuation affects the electron beam that forms the diffraction pattern, so the diffraction pattern does not accurately reflect the structure of the material. Consequently, not only must the blade be manufactured precisely, but it must be clean. Actually, however, the increased complexity of the adopted rotary mechanism also adds to the difficulty of completely eliminating dust, etc. From the standpoint of measurement precision, therefore, diffraction intensity analysis by means of such sectors set in vacuo is undesirable.
Furthermore, although Japanese Unexamined Patent Publication No. 7-6967 discloses an observation device that uses reflection high-energy electron diffraction, it merely suggests a configuration that uses a filter that selectively transmits only light of a specific wavelength. That is, it is based on the idea of handling as a bundle the light incident on the filter, but there is no suggestion of the idea of incrementally varying the light transmittance.